Charles Collinson and Elwood Atherton
The Sylamore Sandstone (Penrose, 1891b, p. 113, 114), the basal Upper Devonian formation in central and western Illinois (Workman and Gillette, 1956), is named for Sylamore Creek, Stone County, central northern Arkansas.
The Sylamore Sandstone is more or less continuous through Missouri, north and west of the Ozark Uplift, to the type locality, and it is correlated with the Hardin Sandstone east of the Ozarks in Kentucky and Tennessee.
Extent and Thickness
The Sylamore Sandstone is widely but sporadically present in Illinois, is rarely more than 5 feet thick, and generally varies from a few inches to a mere thin layer of sand embedded in the base of the Sweetland Creek Shale or the Grassy Creek Shale.
The Sylamore Sandstone is the basal formation of the Upper Devonian Series. In the western part of Illinois, it rests unconformably on the Middle Devonian Cedar Valley Formation or Wapsipinicon Limestone, on Silurian dolomite, or locally on Ordovician limestone. In eastern Illinois it probably is equivalent to thin sandy beds in the upper part of the Blocher Shale and the lower part of the Sweetland Creek Shale.
The Sylamore Sandstone consists of well rounded, fine to medium, quartz sand grains, like those in the older Paleozoic sandstones. It varies from friable sandstone to grains cemented with pyrite, calcite, or dolomite.
PENROSE, R. A. F., JR., 1891b, Manganese, its uses, ores, and deposits: Arkansas Geological Survey Annual Report 1890, 642 p.
WORKMAN, L. E., and TRACEY GILLETTE, 1956, Subsurface stratigraphy of the Kinderhook Series in Illinois: Illinois State Geological Survey Report of Investigations 189, 46 p.
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